Conventional thermal transfer printers of a sublimation type or a fusing type form a color image by overlaying on a recording sheet an ink film having a thin layer of ink of one among three colors cyan, yellow, and magenta or four colors including black arrayed lengthwise one color at a time, and sequentially transferring ink each color cyan, yellow, and magenta (and black) onto the recording sheet by applying heat to the ink film via a thermal head. Furthermore, conventional TA (thermo-auto-chroma) printers form a color image by performing a plurality of image formations at different temperatures corresponding to colors via a thermal head on a special recording sheet having characteristics which are different for an applied color depending on the applied temperature.
In the aforesaid printers, image data input to the printer is subjected to image processing including contrast emphasis, edge emphasis, color correction and the like. High quality images can be produced by outputting image data which has been subjected to such image processing.
The amount of correction performed in image processing is set by the user to produce a desired image after the user visually examines an image output from the printer. Thus, until an image is produced which satisfies the user, it is necessary to repeatedly set the amount of correction performed in image processing and visually examining the output images.
As an example using the aforesaid printer an output device, there are services which output the images of single film frames on paper as positive images in order to readily see a plurality of images on a negative film at a facility for developing photographic film. This type of process is called index printing. The index printing method is briefly described below. Using an image reader (not shown in the drawings), images on the negative film are read frame by frame, subjected to negative-to-positive conversion, and the read image frames input to the printer in frame units. The printer outputs a plurality of input image frames on paper in a layout such as, for example, those shown in FIGS. 4, 5, and 6. Thus, an index print is completed. The previously mentioned negative-to-positive conversion may be accomplished by the image reader, or by the printer, or by a host computer of an embodiment described later. The size of individual image frames of an index print may be varied in accordance with the layout of a plurality of image frames on a single recording sheet. Thus, although image processing corresponding to image frame size is necessary, such image processing corresponding to image frame size is not accomplished in conventional printers.
When forming a plurality of images of different sizes on a single recording sheet, there is a mixture of images subjected to optimum image processing and image not subjected to optimum processing if said image formation is accomplished without changing the amount of correction of image processing when forming images of a single recording sheet. In such circumstances, high quality image formation is not achieved for all images of the recording sheet.